Under Threat

Water Balance

• Rivers and streams are dynamic and constantly change form while maintaining a natural balance. Variables of slope, discharge volume and sediment size influence a stream’s shape.

• Impermeable surfaces, like pavement and buildings, cause water to flow off the land without absorbing into the earth to recharge the groundwater or return to the atmosphere through evaporation or transpiration. The peak flow is greatly impacted by urban development.

• When more than 15% of land area is made up of hard surfaces, like asphalt and concrete, a significant deterioration of the watershed occurs. 

• Monitoring in Twelve Mile Creek indicates that the system has been altered dramatically.

Erosion and Sedimentation

• On the Fonthill Kame and in the Short Hills, the impact of urbanization is magnified by the very steep terrain and the easily eroded soils.

• Sudden, large volumes of surface runoff cause excessive erosion to stream banks and slopes. Fast flowing, high energy water picks up particles and deposits them where the flow is slower and has less energy.

• Floodplains are areas of land adjacent to rivers, where the terrain is not steep and excess water can flow over a large area. The movement is slowed and  sediments drop and settle. 

• A combination of excessive water flow, vulnerable soils and steep slopes have resulted in Twelve Mile Creek disconnecting from natural floodplains as stream channels have eroded and scoured downwards. Without natural floodplains helping to spread the water volume, slow the water speed, and collect carried sediment, erosion and scouring continues. 

• Sediment deposited within the stream can bury the gravel and cobble creek beds that Brook Trout need for spawning and reproduction.

• Turbidity, a measure of the level of suspended paricles in the water, must be low for Brook Trout to survive. They require clear and clean water.

Water Quality & Temperature

• In-stream water warms up when surface rainwater runoff mixes with the cold base flow from groundwater.

• Dark surfaces, like roofs and roads, absorb heat energy from the sun during the day and transfer that heat to stormwater runoff after a rainfall.

• The loss of  tree canopy and dense vegetated buffers along streams allows for greater sun exposure and heating.

• Multiple man-made ponds are connected to Twelve Mile Creek. Exposed to the sun’s radiation, heat transferred to the surface water within these ponds can add warm water to the creeks. It may take over a kilometre for groundwater upwellings to bring down the equilibrium temperature of the stream to a survivable level.

• Fall water temperatures trigger Brook Trout spawning. Females may delay laying eggs if the water is not cold enough (below 12°C is ideal and the maximum temperature for ovulation is 16°C). If delayed for too long the female may abandon spawning for the year.

• Springtime water temperature affects the development rate of newly hatched alevins, as they take longer to mature in warmer water.

• At temperatures above 19°, Brook Trout become stressed due to low oxygen levels. This stress impacts their growth, development and  sexual maturity.

• Temperatures over 22°C for several days in a row could lead to Brook Trout mortality.

• Runoff can carry unseen pollutants like fertilizers, chemicals, pesticides and metals, that have been picked up from roads and fields.

Climate Change

• Climate change is predicted to cause greater fluctuations in the amount of precipitation that falls across Canada, resulting in variable periods of flooding or drought depending on region and season. In the short-term, a small increase in precipitation is projected in all seasons. If global emissions remain high, a larger increase is projected in annual and winter precipitation with a small decrease projected in summer precipitation over large areas of southern Canada.

• The amount of extreme precipitation for a short-duration (a day or less) is projected to increase, with a larger increase corresponding to stronger global warming.

• The frequency and intensity of downpours from thunderstorms may increase and lead to a higher peak flow and greater volumes of water entering Twelve Mile Creek over shorter periods of time.

• Increases to air temperatures could compound the heat impacts to stream temperatures.